EXCESSIVELY WORN LINERS
Over a period of time, cylinder liners become worn simply because of engine operation. The best method of finding excessive wear is to take measurements of the cylinder liner with an inside micrometer caliper. Two
–Liner before and after stoning.
types of liner wear check are illustrated in figure 3-5. Excessive maximum diameter results from general wear equally around the cylinder. Out-of-roundness is produced by the piston thrusting against one or two sides of the cylinders.
Clearance between a piston and a liner is generally checked by measuring both parts with a micrometer. On smaller engines, you can use a feeler gauge. Clearance in excess of that specified by the manufacturer is generally due to liner wear, which normally is greater than piston wear.
To determine liner wear, take measurements at three levels in the liner. Take the first measurement slightly below the highest point to which the top ring travels; take the next measurement slightly above the lowest point of compression ring travel; and take the third measurement at a point about midway between the first two. (Record all readings, so that rapid wear of any particular cylinder liner will be evident.) If wear or out-of-roundness exists beyond specified limits, replace the liner. Figure 3-6 shows two examples of taking
.–Measurements for determining liner wear.
.–Measuring the inside of a cylinder liner.
inside measurements. The liner shown in figure 3-6, view B, requires at least twice as many measurements as other types of liners because it is from an opposed piston.
You will not get accurate measurements unless you
position the caliper or gauge properly in the liner. Common errors in positioning are illustrated in views A and B of figure 3-7. Hold one end of the caliper firmly against the liner wall as shown in view A of figure 3-6. Then move the free end back and forth, and up and down, until you establish the true diameter of the liner. The moving end will trace a patch similar to that illustrated in figure 3-8.
Considerable experience in using an inside micrometer or cylinder gauge is necessary to ensure accuracy. As a precaution against error, it is a good
—Errors to avoid when taking liner measurements.
—Trace of caliper end when determining the true diameter of a liner.
practice for two persons to take the liner measurement; then any discrepancy between the two sets of readings can be rechecked.
Causes
Excessive or abnormal wear of cylinder liners may be caused by insufficient lubrication, dirt, improper starting procedures, or low cooling water temperature.
The lubricating system must be carefully maintained in proper working order. The method of cylinder liner lubrication varies with different engines. The proper grade of oil, according to engine specifications, should be used
The engine must not be operated in a dirty condition. The air box, crankcase, and manifold should be cleaned and maintained in a clean condition, to avoid cylinder wear and scoring. (Attention to the air cleaner, oil filters, and oil centrifuge are the best precautions against the entrance of dirt into the engine.)
Improper starting procedures will cause excessive wear on the liners and pistons. When an engine is first started, some time may elapse before the flow of lubricating oil is completed; also, the parts are cold and condensation of corrosive vapors is accelerated accordingly. These two factors (lack of lubrication and condensation of corrosive vapors) make the period immediately after starting a critical time for cylinder liners. If an independently driven oil pump is installed, it must be used to prime the lube oil system and build up oil pressure before the engine is started The engine should not be subjected to high load during the warm-up period. Follow the manufacturer’s instruction manual concerning warm-up time and load application for the engine concerned The cooling water of an engine should always be maintained within the specified temperature ranges. If the temperature is allowed to drop too low, corrosive vapors will condense on the liner walls.
